1. The Field of the Invention
This invention relates to orthopedic surgical procedures and, more particularly, to surgical devices involved in replacing, reconstructing or securing synthetic or biological connective tissue to a bone surface, such as, for example, attaching and maintaining a replacement anterior cruciate ligament (ACL) against a bone.
2. The Background Art
The knee joint is one of the strongest joints in the body because of the powerful ligaments which bind the femur and tibia together. Although the knee is vulnerable to injury as a result of the incongruence and proximity of its articular surfaces, the knee joint provides impressive stability due to the arrangement and interacting strength of its ligaments, muscles and tendons.
To a layman, the operation of the human knee resembles the actions of a hinge joint. However, in reality, the knee joint provides complicated mechanical movements and maneuverability far more complex than a simple hinge mechanism in regards to the rotation and gliding motions that may occur at the joint. In addition, the motions of flexing and extending the knee (and, in certain positions, the slight rotation inward and outward of the knee), require a very detailed structural configuration to facilitate the associated, refined mechanical movements of the knee joint.
Structurally, the knee joint comprises two discs of protective cartilage called menisci which partially cover the surfaces of the femur and the tibia. The menisci operate to reduce the friction and impact loading between the femur and the tibia during movement of the knee. The knee is also partly surrounded by a fibrous capsule lined with a synovial membrane which secrets a lubricating fluid. Strong ligaments on each side of the knee joint provide support to the joint and limit the side-to-side motion and joint opening of the knee. Fluid filled sacs called bursas are located above and below the patella (kneecap) and behind the knee providing a means of cushioning the kneecap upon impact and helping with joint lubrication. Moreover, the quadriceps muscles run along the front of the thigh to straighten the knee, while the hamstring muscles run along the back of the thigh to bend the knee.
Two intra-articular ligaments of considerable strength, situated in the middle of the joint, are known as the cruciate ligaments. These ligaments are referred to as "cruciate ligaments" because they cross each other somewhat like the lines of the letter "X". The anterior and posterior cruciate ligaments receive their names in respect to the positioning of their attachment to the tibia. The primary function of the anterior cruciate ligament (ACL) is to provide a means for limiting hyperextension of the knee and preventing the backward sliding of the femur on the tibia plateau. The ACL also assists in limiting any medial rotation of the knee joint when the foot is solidly on the ground and the leg fixed in position. Conversely, the posterior cruciate ligament (PCL) primarily provides a means for preventing hyperflexion of the knee and preventing the femur from sliding forward on the superior tibial surface when the knee is flexed.
Although the structure of the knee provides one of the strongest joints of the body, the knee is usually one of the most frequently injured joints. Athletes and persons who perform tasks requiring a great deal of body rotation are the most susceptible to serious ligament stressing and tearing at the knee joint. Consequently, the growing number of ligament injuries has given rise to considerable innovative activity within the area of orthopedic medicine in an effort to create surgical procedures and devices for replacing and reconstructing torn or dislocated ligaments.
Typically the surgical procedures for ligament replacement and reconstruction involve tissues being grafted from one part of the body (autograft) to the original attachment sites of a torn or dislocated ligament. Once the ligament graft has been transplanted, it is then attached to the natural fixation sites of damaged ligament. For example, the replacement of an anterior cruciate ligament (ACL) may involve transplanting a portion of the patellar tendon to the attachment sites of the original ACL to assist in the reconstruction of the ACL in the knee joint.
The expectations of prior art orthopedic procedures typically relate to reconstructing or replacing natural ligaments so as to enable the recipient to return to his or her full range of activity in as short a period of time as possible. To that end, medical researchers have attempted to duplicate the relative parameters of strength, flexibility, and recovery found in natural ligaments of the body. Unfortunately, many of the prior art methods of reconstructing and replacing damaged ligaments have generally proven inadequate for immediately restoring full strength and stability to the involved joint. Furthermore, there has long been a problem of effectively fastening a ligament to a bone surface for the duration of a ligament's healing process, which process involves the ligament graft growing to an adjoining bone mass to restore mobility to the injured joint of an orthopedic patient.
Early ligament replacement procedures traditionally comprised extensive incisions and openings in the knee to attach a replacement ligament to bone surfaces at the fixation sites of the natural ligament. The ends of a grafted ligament were typically secured to exterior bone surfaces by driving stainless steel staples through or across the ligament and into the adjacent bone mass. The legs of the staples are generally adapted for piercing and penetrating tissue and bone mass, while maintaining a ligament at a specified connection site. Other various types of tissue fastening devices, such as channel clamps, were also designed by those skilled in the art. The channel clamps normally differed from the above-mentioned staple arrangement in that the channel clamp fixation devices comprise a plurality of components which do not require clinching in the conventional manner, as when setting a staple into a bone surface.
However, the use of stainless steel staples and other related fixation devices have a number of disadvantages. For example, piercing and puncturing of the ligament by the legs of the staples or other fixation devices may result in serious damage to the cross-fibers of the ligament or tissue. Such damage may cause weakening in the tensile strength of the ligament and result in tearing along the cross-fibers of the ligament under normal physical stress. When puncturing or tearing of cross-fibers occurs, the time required for the ligament to heal increases, which in turn results in a significant extension in the amount of time required to rehabilitate the knee joint before allowing the patient to return to normal daily activities.
To alleviate the disadvantages of cross-fiber damage exhibited by staples and other related fixation devices that puncture the body of the ligament, improvements in the types of surgical devices and techniques were developed by those skilled in the art. For example, one such technique involves drilling a hole through a bone to form a channel wherein an anchoring device may be inserted with a ligament graft attached thereto. Typically, the ligament is maintained at a fixation site in the bone channel by passing a suture through one end of the ligament graft and thereafter attaching the other end of the suture to an anchoring device positioned at the face of the opening of the channel in the bone mass. However, problems materialize when trying to secure the threads of the suture to the anchoring device when a physician is working in restricted or confined areas. As a result, combination drilling devices operably coupled to suture anchors were designed for dealing with ligament placement problems in areas of restricted maneuverability.
After a period of time, significant disadvantages emerged wherein a number of the ligament grafts retained in bone mass by the combination drilling/anchor devices began to rupture and tear at their fixation sites around the area where the ligament was in direct contact with the sharp outer edges of the opening of the channel formed in the bone. For example, as replacement ligaments tolerate the stress and strain associated with normal physical activity, the ligament generally begins to fatigue when wearing against the sharp outer edges of a bone channel opening. This form of fatigue typically causes significant damage to the ligament by tearing or cutting into ligament cross-fibers, thus, weakening the connection of the replacement ligament at its reattachment site. Consequently, after a period of time, cross-fiber fatigue, commonly known as "sun-dial" wear, may further result in dislocating the replacement ligament from its original fixation site.
Because of the significant disadvantages associated with "sun-dial" wear or fatigue on replacement ligaments, improved surgical procedures were developed offering arthroscopic-assisted techniques typically including the formation of passages or tunnels through bone mass, wherein natural or synthetic ligaments may be inserted. After the ligament graft has been inserted into the bone tunnel, a ligament anchoring device is generally used to connect one end of a ligament to the exterior of the bone mass. The anchoring means generally requires that the replacement ligament end or ends be advanced beyond the bone tunnel, with each ligament end being bent and secured onto the exterior surface of the bone. Nevertheless, unfavorable disadvantages of ligament bending was observed by those skilled in the art as typically resulting in a force concentration at the location of the ligament bend generally causing the cross-fibers of the ligament to weaken, potentially subjecting the ligament to the possibility of further tearing or rupturing, as in the case of ligament sundial wear.
In response to the problems associated with maintaining a replacement ligament graft at a fixation site, additional devices and techniques were developed offering means whereby a ligament may be retained within a bone tunnel by an endosteal fixation device, such as, for example, an interference screw. The threads of the interference screw are typically bored into the bone tunnel for recessed engagement with the attached bone and one end of the ligament graft, while maintaining the ligament at a fixation site within the bone tunnel. Unfortunately, puncturing, piercing and possible tearing generally results to the cross-fibers of the ligament when the ligament is in direct engagement with the sharp threads of the interference screw. In addition, the interference screw typically requires a ligament replacement graft to be attached to its original bone.
During flexion or extension of the ligament, tension loads tend to act against the fixation site of the ligament generally causing strain on the ligament against its fixation site. Under such strain, the facing of the threads of the interference screw generally effect a pinching or piercing of the ligament which may cause tearing or dislocation of the replacement ligament under the stress associated with normal physical activities. Consequently, when a grafted ligament suffers cross-fiber damage due to puncturing, piercing or tearing, the healing period for the ligament dramatically increases, thereby in effect, increasing the rehabilitation time for the patient to recover.
One of the preferred methods employed by a number of skilled physicians when repairing torn or dislocated ligaments involves the harvesting of an autograft patella tendon bone block for incorporation into a femoral socket. Although the use of a patella tendon bone block provides a number of advantages, especially when dealing with fixation of the replacement ligament, the harvesting of a patella bone block typically results in extensive morbidity to the knee joint, requiring a considerable amount of time for the knee joint to heal, before a patient can resume any normal physical activity.
As illustrated by the foregoing summary, efforts are continuously being made to improve the graft types, surgical methods and devices used in replacing and reconstructing torn or dislocated ligaments so as to make the process more efficient and effective. However, significant disadvantages remain with all the presently known devices and methods offered by the prior art.